Barium glass having low power factor



Patented Jan. 22, 1946 UNITED "STATEQMBATENT' OFFICE BARIUM GLASS HAVINGLOW rowan moron William Houston Armistead, Jr., Corning, N. Y.

assignor to Corning Glass Works, Corning,

N. Y.', a corporation of New York No Drawing. Application July 11, 1944,

" a Serial No.- 544,4fi7

(cl. roe-54) 6 Claims.

This invention relates to glass compositions and has for its primaryobject to provide a new and useful glass having certain specialcharacteristics making it particularly suitable as an insulating mediumfor use in electrical condensers for radio circuits. A glass. havingthese characteristics would be a welcome substitute for mica which isordinarily used for this purpose and which is expensive and requiresconsiderable selection to insure suitable uniformity in, quality. Glass,on

the other hand, can be manufactured relatively cheaply and with greatuniformity in composition and properties. However, no glass hasheretofore been devised which combines the'desired characteristics tothe extent that does the glass I herein claimed.

The desired characteristics are:

A power factor less than 07%, as measured at a frequency of onemegacycle at room temperature.

A dielectric constant of at least 4. 4 A temperature coeflicient lessthan 100 parts per million per degree centigrade. By temperaturecoefficient is meant the rate of change of dielectric constant withchange of temperature.

- every 1% is not substantially changed. This result is entirelyunexpected, because the introduction of alumina into analkali-containing borosilicate raises the power factor by as much as 02%for of alumina. The presence of alumina is so efiectivein maintaining alow power factor,

a high dielectric constant and low temperature coefficient that thesilica content can be reduced to a low value or even omitted withoutlosing the This is an important requirement since it is desirable thatthe capacity of a condenser should not change appreciably over thetemperature range in which it is to be used. Most glasses do not meetthis requirement.

A softening-temperature not greater than 800 C., being that temperatureat whichv a thread of glass one millimeter in diameter and twentythreecentimeters long will elongate at the rate of one millimeter per minutewhen heated throughout the upper nine centimeters of its length.

Any and all of these properties may easily be obtained at the sacrificeof others. Many glasses are known which have low power factors but theylack one ormore of the above mentioned properties and hence have notbeen entirely suitable for use in the insulation of condensers forcircuits carrying radio frequency currents. In such circuits the powerlosses caused by lack of these properties may be quite substantial. Theprob-- lem solved by. me has been to obtain all of the desiredproperties in one glass.

Pure silica has a very low power factor and also a sufliciently lowtemperature coeflicient for r the present purpose but the high fusingpoint of silica and its extremely high viscosity when fused are wellknown and preclude its present use. I have found that, when silica isfluxed with boric oxide and barium oxide, compositions may be benefit ofmy invention.

In general, my new glasses consist of a homogeneous mixture of 10% to30% BaO, 5% to 20% AlzOa, 22% to 80% B203, and 0% to SiOa. Thesecompositions have power factors less than 07%, dielectric constantsgreater than 4, temperature coemcients less than 100 P. P. M. per degree(3., andsoftening points less than 800 C. If desired, the softeningpoints and power factors can be lowered somewhat further by theintroduction of fluorine, preferably by the addition of 5% to 10% ofbarium fluoride in lieu of. barium oxide.

As examples of glasses in accordance with my invention, the followingcompositions, calculated in percent by weight from their respectivebatche together with their properties are given:

Eco. 20 20 20 20 20 30 10 .10 A110; 5 10 15 20 l0 l0 l0 10 13,0; 75 7005 50 30 30 B101. 20 30 50 BaF; 10 Power factor, percent .056 .048 .048.048 .045 .070 .045 .045 Dielectric constant. 4 4. 8 5. 0 5. 3 5. 0 6. 04. 5 4. 8 Temp. coed.

per: 70 70 7O 70 64 70 Softening temp., C.. 550 563 580 600 628 744 797555 Expans1oncoeif. l0". 72 71. 70 68 57.0 54.3 39.5 71

ards for 1942. COmparisonOf glasses 1, 2, 3 and phases and renders allA1203, 22% to 80% 32%,

4 shows that power factor decreases or remains constant and dielectricconstant increases with increase in alumina. Composition 8 containsbarium fluoride and shows a slight decrease in power factor andsoftening point over composition 2 which contains no fluorine but isotherwise similar to composition 8.

1. A glass having a power factor less than 07%, a dielectric constantgreater than 4, a. temperature coefiicient less than 100 partspermillion per degree 0., a softening point less than 800 C., andconsisting of compounds of barium, aluminum, boron and silicon inproportions equivalent to 10% to 30% B90, 5% to 20% and to 55% SiOz.

2. A glass having a power factor less than .07%, a dielectric constantgreater than 4, a temperature coefiicient less lion per degree (3., asoftening point less than 800 0., and consisting of 10% to 30%-B520, to20% A1203, 22% to 80% B203, and 0% to 55% SiOz.

3. A glass having a power factor less than 07%, a dielectric constantgreater than 4, a temperature coemcient less than 100 parts per millionper degree 0., a softening point less than than 100 parts per mil- 8000., and consisting of compounds of barium, aluminum, boron. and siliconin proportions equivalent to 10% to BaO, 5% to 20% A1203, 22% to 80%B403. and 0% to SK): and a small amount of fluorine.

4. A glass having a power factor less than .07,%, a dielectric constantgreater than 4, atemperature coeflicient less than 100 parts per millionper degree 0., a, softening point less than 800 0., and consisting of10% to 30% B110, 5% to 20% A1203, 22% to B203, and 0% to 55% S102, andshowing by analysis the presence of fluorine.

5. A glass having a power 'factor less than 07%, a dielectric constantgreater than 4, a temperature coeflicient less than parts per millionper degree 0., a softening point less than 800 0., and consisting ofapproximately 20% B80, 10% A1203, 50% B203, and 20% S102.

6. A glass having a power factor less than 07%, a dielectric constantgreater than 4, a temperature coeflicient less than 100 parts per mil-=lion per degree 0., a softening point less than 300 0., and consistingof approximately 10%, mm, 10% A1203, 30% B203, and 50% S102.

WILLIAM HOUSTON ARMISTEAD, JR.

